1. Field of the Disclosure
The present disclosure relates generally to catalyst materials and processes for making and using them. More particularly, the present disclosure relates to metal oxide catalyst materials useful, for example, in the ammoxidation of propylene or isobutylene, processes for making them, and processes for making acrylonitrile and methacrylonitrile using such catalysts.
2. Technical Background
Molybdenum-iron-bismuth oxide catalysts have conventionally been used for the reaction of propylene or isobutylene with ammonia and oxygen to make acrylonitrile or methacrylonitrile. Such “ammoxidation” reactions are typically performed at high temperature in the gas phase, often in fluidized bed reactors. The catalyst materials themselves often include a variety of additional elements, such as cerium, cobalt, potassium, cesium, chromium, antimony, as promoters to increase the catalytic efficacy of the catalytic material. The catalyst materials are conventionally made in a batch process by coprecipitation of metal containing precursors such as nitrates with ammonium molybdate, followed by spray-drying of the resulting slurry and calcining of the resulting particles to provide oxide material. More complex multiple-step preparations are also known.
Ammoxidation catalysts are typically made with on the order of 50 wt % silica as a carrier material. Such catalyst materials can be made by coprecipitation in the presence of a silica sol, followed by spray drying and calcining as described above. The silica helps to bind the catalyst material, thus improving attrition resistance (e.g., resistance to breakage due to collisions in a fluidized system). Attrition resistance is a key parameter for catalysts to be used the fluidized bed systems typically used in ammoxidation processes.
There remains a need for improved ammoxidation catalysts that provide not only acceptable attrition resistance, but also desirable activity (e.g., overall reaction of propylene or isobutylene starting material) and desirable selectivity (e.g., fraction of reacted starting material converted to acrylonitrile or methacrylonitrile).